Classification of Pain
Acute Pain
Pain immediately following an injury to the body is considered to be acute pain, whereas pain lasting beyond the expected healing time, or persistent pain that does not respond to usual pain control methods, is defined as chronic pain. Acute pain serves a useful purpose in minimizing the extent of injury by causing an organism to recoil from a noxious or harmful stimulus. In most cases, the objective physical findings associated with acute pain can be localized directly to the site of injury. Injury to nerves on visceral organ systems can present as diffuse, poorly differentiated, referred pain.
Acute pain is usually self-limiting and typically subsides when the injury heals. Untreated or inadequately treated pain can evoke physiologic hormonal responses that alter circulation and tissue metabolism; these can also produce tachypnea, tachycardia, widening of the pulse pressure, and increased sympathetic nervous system activity. Inadequately treated pain can produce significant psychological stress responses and compromise the body's immune system by provoking release of endogenous corticosteroids. Decreased range of motion, diminished pulmonary vital capacity, and a compromise in the overall well-being of a person secondary to poorly treated pain can delay recovery after surgery or trauma. Acute pain is often exacerbated by anxiety and secondary reflex musculoskeletal spasms.
Acute pain should always be aggressively managed, even before a definitive cause is known. In patients with traumatic head injury, medications should be withheld until a full neurologic workup can be performed because they can interfere with cognitive function. Patients with acute abdominal pain also may have pain medications withheld until a diagnosis is made; however, several studies support early pain management.22,23 When pain is relieved, the patient is more comfortable and better able to cooperate with the history, physical examination, and diagnostic procedures. Postoperative and other acute pain syndromes often are ignored or inadequately treated, however. Part of the tendency to undertreat pain is the reluctance of caregivers to prescribe opiates for fear of causing addiction. Addiction to opioids is essentially nonexistent when these drugs are prescribed for acute pain, and withholding appropriate pain treatment causes needless patient suffering.
Chronic Pain
The origins of chronic pain may be neurogenic, nociceptive, psychiatric, or idiopathic. As will be presented later, it is important to further differentiate chronic pain syndromes into those that are associated with malignancy from those that are not. All forms of chronic pain share some common characteristics, however. Unlike acute pain, which prompts the afflicted individual to avoid further injury or seek help, chronic pain usually serves no benefit to the individual. Chronic pain can be episodic or continuous, or a combination of both. A patient may feel constant pain and also experience exacerbations of more intense pain at various times. Chronic pain can cause a person to feel “trapped” inside of his or her body, distinguished only by more painful and less painful days. Chronic pain often is destructive to the host by deteriorating quality of life, functional ability, spiritual and psychological well-being, interpersonal relationships, and financial status.17 Chronic pain also can cause changes in appetite, psychomotor retardation, irritability, social withdrawal, sleep disturbances, and depression. The patient often cannot remember an existence free of pain and is convinced that the pain will be present until death. In short, chronic pain can become an all-consuming focus of the patient's life.
The key to successful chronic pain management rests on prevention and elimination of unnecessary suffering and despair. Chronic pain management should consider the applicability of cognitive interventions (relaxation technique, self-hypnosis, psychiatric therapy) as well as physical manipulations (local application of heat, cold, massage, electrical nerve stimulation, acupuncture, and physical therapy). Pharmacologic agents (antidepressants, antiarrhythmics, anticonvulsants, major tranquilizers, and longer-acting opioids), regional anesthesia (local anesthetic blocks with or without corticosteroids or chemical neurolysis), surgical interventions (spinal decompression, release of nerve entrapment), and spinal analgesia (intraspinal opioids or local anesthetic agents) are also warranted.24,25
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